The present invention relates to varaiable speed pulley, and more particularly to a spring-locked speed change pulley used as a drive device in an automobiles, motorcycle, agricultural machine, or other industrial machine.
Recently, a variety of varaiable speed pulleys of this type have been disclosed, for instance, in Japanese Published Utility Model Applications No. 35421/1977, Japanese Laid-Open Utility Model Application (Kokai) No. 122847/1984, and Japanese Laid-Open patent application (Kokai) No. 79355/1982. In these varaiable speed pulleys, a pair of V-shaped pulley pieces are mounted on a shaft in such a manner that either the two pulley pieces or only one pulley piece is rotatable around the shaft and movable along the shaft. A stopper is fixedly mounted on the shaft, located beside the one movable pulley piece or each of the two movable pulley pieces. A coil spring is interposed between the movable pulley piece and the adjacent stopper to absorb the torque which is developed during operation. With this arrangement, even under severe operating conditions, the variation in the effective diameter of the varaiable speed pulley employed as the drive or driven pulley and the belt tension established by a tension pulley or idler are automatically, effectively and positively adjusted.
In the varaiable speed pulley disclosed by Japanese Published Utility Model Application No. 35421/1977, as shown in FIG. 1 herein, the coil spring is wound in the direction that it is wound as the pulley rotates, the both ends of the spring are bent and engaged with holes formed in the movable pulley piece and a shaft cylinder provided on the side of the movable pulley piece. Accordingly, when the movable pulley piece is rotated repetitively in the forward and reverse directions by the variations of torque, the ends of the spring may be broken.
In the varaiable speed pulleys disclosed by Japanese Laid-Open patent application No. 79355/1982 and Japanese Published Utility Model Application No. 122847/1982, as shown in FIGS. 2 and 3 herein, respectively, both ends of the spring are abutted against engaging protrusions or fitted in tapered grooves. Therefore, in these variable speed pulleys, unlike the above-described ones, the ends of the spring will not be broken. However, because the spring is only unwound, it cannot transmit a torsional torque developed between the stopper and the movable pulley piece in the forward or reverse direction. Thus, that variable speed pulley suffers still from the difficulty that is very limited in its range of application.